Assad regime forces on Sunday killed nine civilians, including four children, in air and land attacks targeting the opposition-held enclave of Eastern Ghouta, according to a Syrian civil defense group.

In the town of Misraba, eastern Ghouta, airstrikes targeting residential areas killed four civilians, including a child, a civil defense official said on condition of anonymity due to security concerns.

Artillery fire also hit residential areas in besieged Eastern Ghouta, killing four civilians, including three children in the town of Merc and another in Sakba.

Eastern Ghouta falls within a network of de-escalation zones -- endorsed by Turkey, Russia and Iran -- in which acts of aggression are expressly prohibited.

Nevertheless, the Syrian regime continues to target residential parts of the city, killing at least 539 people -- and injuring more than 2,000 others -- since Dec. 29 of last year.

Home to some 400,000 civilian residents, Eastern Ghouta has remained under a crippling regime siege for the last five years.

Syria has only just begun to emerge from a devastating conflict that began in 2011, when the regime cracked down on demonstrators with unexpected ferocity.